Optical communication system and method for installing it

ABSTRACT

An optical signal communication system employs an optical signal conduit that is threaded through segments of a utility pipe, such as a water main. Water-tight optical signal transfer fittings are used so that the optical signal conduit does not need to run through valves in the water main.

BACKGROUND OF THE INVENTION

[0001] The present invention is directed to an optical communication system in which optical fibers or fiber cables are installed underground without the need to destroy streets or disrupt traffic by digging long trenches.

[0002] A familiar irritation to commuters in many cities is that the installation of optical cables frequently disrupts traffic because trenches need to be dug in the streets in order to bury the cable. In some cities, the same streets can be disrupted more than once when competing companies install optical cables.

[0003] This troublesome installation process permits downtown businesses to enjoy the vast bandwidth afforded by optical fibers. The optical communication system, though, rarely extends into residential sections of a city. Consequently, people in residential sections are usually unable to benefit from the high bandwidth of optical fibers. Unless a homeowner is willing to pay for cable television, a satellite receiver, or a digital subscriber line, he or she is limited to low-bandwidth communication over the telephone lines. Low-bandwidth communication is becoming increasingly undesirable as use of the internet spreads and the audio and visual content of internet sites increases. One occasionally hears that the United States is blessed with a magnificent, high-bandwidth communication system except for “the last mile” between telephone central offices and individual residences. The low bandwidth of this last mile acts as a bottleneck between homeowners and the nation's high-speed communication network.

SUMMARY OF THE INVENTION

[0004] An object of the invention is to provide a method for installing an optical communication conduit, either a single fiber or a cable of fibers, without excessively damaging the streets or tying up traffic for long periods of time.

[0005] Another object is to provide an optical communication system that serves residential areas.

[0006] A further object is to increase revenues that are available to municipalities, without increasing taxes, by permitting public utility pipelines to provide a communication service in addition to their primary service.

[0007] These and others objects which will become apparent in the ensuing detailed description can be attained by threading optical communication conduits through utility pipelines, such as water mains. Valves and other potential obstructions can be avoided by using water-tight optical signal transfer fittings that permit optical signals to pass through pipe walls.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 schematically illustrates an optical communication system in accordance with the present invention;

[0009]FIG. 2 illustrates how an optical communication conduit can be threaded through a section of a pipeline;

[0010]FIG. 3 is a cross-sectional view illustrating an example of a water-tight optical signal transfer fitting;

[0011]FIG. 4 is a side view of the water-tight optical signal transfer fitting shown in FIG. 3;

[0012]FIG. 5 is a top view of a base member employed in the fitting shown in FIG. 3;

[0013]FIG. 6 is a side view of a sealing unit employed in the fitting of FIG. 3;

[0014]FIG. 7 is a perspective view of a sealing member inside the sealing unit shown in FIG. 6; and

[0015]FIG. 8 is a perspective view of a spring for taking up slack in an optical communication conduit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016]FIG. 1 illustrates an optical communication system 10 in accordance with the method of the present invention, in which a conduit for optical signals is threaded through a utility pipeline in order to reach customers.

[0017] In FIG. 1, a water tower 12 has a pedestal portion 14 that supports a tank portion 16 above the surface 18 of the ground. The tank portion 16 supplies water to customers of a utility company via a municipal water-distribution system that includes a water main 20. The water main 20 includes valves 22, 24, 26, 28, 30, and so forth that permit pipe sections 32, 34, 36, 38, and so forth to be isolated from one another. Although not shown in FIG. 1, the water main 20 supplies water to customers 40, 42, 44, and so forth.

[0018] An optical communication station 46, which may be located at a central office in the public telephone network, includes an electro-optic converter 48 that receives digital signals in electronic form and converts them to corresponding optical signals that are emitted to an optical fiber 50. It also includes an opto-electric converter 52 that receives optical signals in digital form from an optical fiber 54, and converts them to corresponding electrical signals. The fibers 50 and 54 are connected to an optical coupler, such as splitter-combiner 56. The splitter-combiner 56 sends and receives signals from a segment 58 of an optical signal conduit 60. The optical signal conduit 60, in the example shown in FIG. 1, is a single-fiber conduit. Optical signals are transferred through the wall of pipe section 32 for communication between the segment 58 and a segment 62 of the optical signal conduit 60 that lies within pipe section 32 by way of a water-tight optical signal transfer fitting 64.

[0019] The optical signal conduit 60 also includes a segment 66 within the pipe section 34, a segment 68 within the pipe section 36, and a segment 70 within the pipe section 38. Watertight optical signal transfer fittings 72 and 74 are provided in the water main 20 on either side of valve 24 to permit transfer of signals between segments 62 and 66 of the optical signal conduit 60 by way of a bypass segment 76. Similarly, water-tight optical signal transfer fittings 78 and 80 are provided on either side of valve 26 to permit communication between segment 66 and a segment 82, and between the segment 68 and a segment 84. The segments 82 and 84 of the optical signal conduit 60 are connected to a local signal distribution unit 86 that serves the neighborhood where customers 40-44 and others in this neighborhood, indicated schematically in FIG. 1 by dotted line 88, dwell. In the example shown in FIG. 1, the local unit 86 comprises an optical coupler, such as splitter-combiner 90, which may be a star coupler. The splitter-combiner 90 is connected by optical fibers (not numbered) to the customers.

[0020] With continuing reference to FIG. 1, customer 40, for example, has electrical equipment that includes an electro-optic converter 92 and an opto-electric converter 94 that are connected by optical fibers (not numbered) to an optical splitter-combiner 96. In this manner, the customer 40 can receive optical signals from the conduit 60 and transmit optical signals to the conduit 60.

[0021] By now, it will have become clear that reference numbers 98 and 100 identify watertight optical signal transfer fittings on either side of valve 28 to permit transfer of optical signals to and from a local signal-distribution unit, such as splitter-combiner 102, that serves another neighborhood. Additional water-tight optical signal transfer fittings are provided at valves further downstream in water main 20 or at sharply angled branches in the in the water main 20. These water-tight optical signal transfer fittings permit connection to either local signal distribution units or to bypass segments of the optical signal conduit if the valves or branches are located at areas that do not need local signal distribution units. Water-tight optical signal transfer fittings need not be used only at valves and branches, of course; they can be installed in the water main anywhere local signal distribution units are needed.

[0022]FIG. 2 illustrates how the optical signal conduit 60 is threaded through the water main 20. To install the segment 66 in the pipe section 34, a hole 104 is dug in the ground 18 at the location of valve 24, and a hole 106 is dug at the location of valve 26. The valves 24 and 26 are then closed. A hole 108 is then bored through the pipe wall near valve 24, and a hole 110 is bored near valve 26. Depending upon the type of water-tight optical signal transfer fittings that will be used, the holes 108 and 110 may then be threaded with a threading tool. A pushing or pulling tool, such as a metal guide strip 112 with a clamp 114 at its end, is then introduced into the pipe section 34 through the hole 108. The guide strip 112 is advanced through the pipe section 34 until the clamp 114 reaches the hole 110, whereupon a workman pulls the clamp 114 out through hole 110 and joins an optical signal conduit 116 to the guide strip 112 by way of the clamp 114. The guide strip 112 is then withdrawn, dragging with it the conduit 116.

[0023] Although FIG. 2 shows a coil for the guide strip 112 at hole 104 and a coil for the optical signal conduit at hole 106, both coils may be located at the same hole if the optical conduit 116 is to be pushed, instead of pulled, through the pipe section 34.

[0024] One example of a water-tight optical signal transfer fitting will now be described with the aid of FIGS. 3-7.

[0025]FIG. 3 is a sectional view illustrating the fitting 74 through the wall of pipe section 34 (see FIG. 1). The fitting 74 is screwed into the hole 108 (FIG. 2) in pipe 34, so the hole 108 would be threaded before the optical signal conduit (in this case, segment 66 of the conduit—see FIGS. 1 and 2) is installed.

[0026] The fitting 74 includes a base member 118 having a threaded portion 120 at one end and a threaded portion 122 at the other end. Between these threaded portions lies a hexagonal portion 124 for engagement by a wrench, and a collar portion 126 for the wrench to rest against. A hexagonal well 128 is provided at the end having threaded portion 120, and a passage 130 extends from the bottom of the well. The passage 130 flares outward as it nears the end of threaded portion 122 in order to avoid sharply bending the segment 66 of the optical signal conduit 60.

[0027] The fitting 74 also includes a hollow cap member 132 having an internal threaded portion 134 so that the cap member can be screwed onto the threaded portion 120 of the base member 118. Externally, the cap member 132 has a hexagonal portion 136 for engagement by a wrench, and a collar portion 138 that is located adjacent the hexagonal portion at the mouth of the cap member 132. A projection 140, with a passage 142 through it, is provided at the other end of cap member 132. An inner portion 144 of the projection 140 is threaded, while an outer portion 146 is rounded. A nut-type clamping element 148 is screwed onto the threaded portion 144 in order to clamp the flared outer end of a copper tube 150 against the rounded portion 146. Although not shown, the copper tube 150 extends to the signal distribution unit 86 (see FIG. 1) and protects the optical signal conduit from physical damage.

[0028] With reference next to FIGS. 3 and 5-7, the fitting 74 also includes a sealing unit 152. It is comprised of four elements: a pair of open-mouth casing members 154 and 156; a turnbuckle member 158 for drawing the casing members together; and a cylindrical sealing member 160 that is made of a pliable polymeric material, such as rubber, disposed within the casing members. The exterior configuration of members 154-158 is shown in FIG. 6 (some of the features discussed below are present but not numbered in FIG. 3 in order to avoid obscuring the drawing with a tangled network of reference numbers and lead lines). The outer portion 162 of casing member 156 is hexagonal so that it will fit within the well 128 (see FIGS. 3 and 5) of base member 118 without rotation. The inner portion 164 of member 156 is threaded. Similarly, the inner portion 166 of casing member 154 is threaded. However, the threads run in opposite directions so that the casing members are either pulled together or pushed apart when turnbuckle member 158 is rotated, depending upon the direction of rotation. The outer portion 168 of casing member 154 is cylindrical. Between its inner and outer portions, the casing member 154 has a hexagonal portion 170 for engagement by a wrench and a collar portion 172. The turnbuckle member 158 itself is hexagonal, again for permitting it to be gripped by a wrench. Although not shown in FIG. 6, the ends of outer portions 162 and 168 have holes for passage of the optical signal conduit.

[0029]FIG. 7 illustrates the sealing member 160 in its initial, undistorted shape. In its initial state, it has a bore 174 through it.

[0030] The installation of the fitting 74 will now be described, primarily with reference to FIG. 3, but with occasional mention of features that are shown in other figures. After segment 66 of the optical signal conduit has been drawn through bore 108, as discussed above, its end is pulled far enough to reach the local signal distribution unit 86 (see FIG. 1). The base member 118 is then threaded onto the segment 66 and screwed into the bore 108. A polymeric washer 176 is then threaded onto the segment 66 and deposited at the bottom of the well 128. Next, the sealing unit 52 is assembled. To do this, the sealing member 160 is placed coaxially within the turnbuckle member 158, and the casing members 154 and 156 are placed over the projecting ends of the member 160, with the turnbuckle member 158 then being rotated enough to draw the casing members together without compressing the sealing member 160. FIG. 3 illustrates that the casing members 154 and 156 have holes at their outer ends, although these holes are not numbered in order to avoid obscuring the drawing. These holes are in alignment with the bore 174 (see FIG. 7) in the sealing member 160 so that the sealing unit 152 can be threaded as a body onto the segment 66. The hexagonal portion 162 (see FIG. 6) of casing member 156 is deposited in bore 128, and a workman then draws the casing members 154 and 156 together using wrenches that grip the turnbuckle member 152 and the hexagonal portion 170 (see FIG. 6) of the casing member 154. The sealing member 160 is compressed by the casing members 154 and 156 as they are drawn together. FIG. 3 shows outward bulges at the holes (not numbered) at the ends of the casing members, and an annular bulge at their mouths. These are incidental consequences, though. The true importance of the compression is that it collapses the bore 174 (see FIG. 7) against the segment 66 of the optical signal conduit 60. This, together with the sealing effect of washer 176, keeps water from leaking from the main.

[0031] A Teflon™ washer 178 is then deposited in a cylindrical bore (not numbered in FIG. 3) in the cap member 132 and, together, they are threaded onto the segment 66. The cylindrical outer portion 168 (see FIG. 6) of casing member 154 fits within the bore. The cap member 132 is then screwed onto the threaded portion 120 until resistance is countered, whereupon the hexagonal portion 136 is engaged by a wrench to further tighten the cap member and thereby create a seal at washer 176. Finally, the clamping element 148 is inserted onto a segment of copper tubing 150, the outer end of the tubing 150 is flared with a flaring tool, the segment 66 is poked through the copper tube 150, and the clamping element 148 is tightened with a wrench.

[0032] The fitting 74 described above is but one type of a water-tight optical signal transfer fitting that can be used with the present invention. Many modifications are possible. For example, the function of sealing unit 152 could be implemented in various ways. One way would be to replace the sealing unit 152 with a hollow member that is threaded onto the segment 66 and then filled with quick-setting epoxy or other potting material. Instead of running the segment 66 all the way to the local signal distribution unit 86, the segment 66 could terminate at a screw-on or bayonet-type connector that is mounted on the water-tight optical signal transfer fitting. The water-tight optical signal transfer fitting need not be screwed into a threaded bore in the pipe section 34; instead, it may be clamped over an unthreaded bore (with a gasket being used between the clamp and the pipe section 34 in order to avoid leakage). The segment 66 of the optical signal conduit need not even extend through the bore (108 or 110) in the pipe section 34, whether to the local signal distribution unit 86 itself or to a connector that is mounted on the fitting. Instead, the water-tight optical signal transfer fitting may have a transparent window, with the end of segment 66 facing the window from inside the pipe section 34. Another alternative would be to join the end of segment 66 to an optical connector before the segment 66 is threaded through the pipe section 34. The optical connector could then be used with a water-tight optical signal transfer fitting which clamps the optical connector either inside or outside of the pipe section 34. A hydroscopic material, such as compressed cellulose, could also be used to prevent leakage.

[0033] In this example, the segment 66 of the optical signal conduit 60 was a single fiber. This fiber may be unjacketed. The lack of a jacket increases the risk that the fiber might be damaged during installation, but after installation the wall of the pipe far exceeds the protective capacity of a jacket. The absence of a jacket would be desirable if there is a risk of any public fear that the material of the jacket might leach into the public water supply and cause a health risk. An unjacketed optical fiber, on the other hand, is just glass, and even the most cautious advocates of public safety would be hard-pressed to find any reasonable basis for alleging a health risk. As for the durability of an unjacketed fiber, the solubility of glass in water is extremely slight.

[0034] In addition to allaying the possibility of public fear of a health risk, the minute diameter of an unjacketed fiber means that any reduction in the effective diameter of the water main for purposes of carrying water would be quite negligible.

[0035] It is desirable that the segment 66 of the optical signal conduit 60 within the pipe section 34 not be so slack that a loop of the segment 66 might be carried by water current to a position where the loop might be broken by a valve, should it be necessary to close the valve (e.g., during repair of the water main 20). One solution to this potential problem is illustrated in FIG. 8. This shows a coil spring 180 made from a stiff plastic tube with holes 182 drilled in it to reduce resistance to the flow of water. The segment 66 would be inserted into the tube during the installation process illustrated in FIG. 2. It will be apparent that the diameter of the spring can be much larger than the diameter of the bore (108 or 110) in the pipe section 34 if the spring itself is “corkscrewed” through the bore. Another possibility, one that is not illustrated, would be to attach short, straight segments of metal coil springs at the outlet of passage 130 (see FIG. 3) of the water-tight optical signal transfer fittings. These spring segments would be coaxial with the passage and would jut into the pipe section 34 by a distance slightly shorter than the diameter of the pipe section. The length of the segment 66 within the pipe section 34 could then be adjusted during the installation process to draw the ends of the springs at opposite bores toward one another, placing the segment 66 in mild tension.

[0036] Other alternatives concern the local signal distribution units 86 (see FIG. 1). Instead of using splitter-combiners that are connected to the equipment of customers by optical fibers, opto-electric and electro-optic converters could be provided in the unit 86 in order to permit local distribution electronically, perhaps by way of coaxial cables. Another alternative would be to install radio transmitters/receivers at the units 86 so that they could cover a neighborhood by radio. Spread spectrum radio units would be a particularly attractive alternative because the transmitter/receiver units at the customers' locations would typically remain permanently positioned. This factor would considerably reduce the problem of controlling the customers' transmission power that occurs in cellular telephone systems which employ spread spectrum. With a spread spectrum radio unit in the local signal distribution unit 86, it would only be necessary to emit a signal that turns a particular customer's transmitter off if that customer has adjusted his transmitter so that the received power level at the unit 86 is too high.

[0037] It will be apparent to those skilled in the art that the optical communication system and method disclosed herein could readily be adapted for use with wavelength division multiplexed optical signals. It makes no difference to the segments of optical signal conduits in the pipe segments or to the method illustrated in FIG. 2 for installing them in the pipe sections whether or not the optical signals themselves are multiplexed.

[0038] The discussion of FIG. 1 used an optical communication station 46 at a central office or switching station of the public telephone system as an example. However, the station 46 could be employed at different types of facilities. For example, the stations 46 could be employed by internet service providers, internet access points, cable television companies (except, of course, that “cable” would be a misnomer here since it would imply distribution by coaxial cable, rather than by optical conduit), and so forth.

[0039] Furthermore, the above discussion has used water mains as only one example of pipelines employed by public utilities. Optical signal conduits could also be threaded through sewer pipes or gas pipes. For long distances, oil pipelines could be employed.

[0040] Although the arrangement shown in FIG. 1 employs a single fiber as the optical signal conduit, it will be apparent to those skilled in the art that the techniques disclosed herein could also be used with an optical signal conduit in the form of a cable comprised of a number of fibers.

[0041] In the installation procedure illustrated in FIG. 2, an optical signal conduit is threaded through a pipe segment and then cut to the desired length. It would also be possible to manufacture optical signal conduit segments having predetermined lengths and to attach screw-together or bayonet-type connectors to the segments at the factory, instead of in the field. An optical signal conduit of this type could be jacketed with material that provides one or more springs, in the manner of FIG. 8, so that the conduit could be used to span a range of distances between valves. The jacket material adjacent the connectors could also be flared outwardly to provide built-in washers that can be squeezed through the bore holes and permit the use of particularly simple water-tight optical signal transfer fittings.

[0042] While the foregoing discussion has concentrated on the use of water-tight optical signal transfer fittings adjacent valves, they may be used elsewhere. The possibility that they could be used adjacent branches in a water main (in order, for example, to avoid the problem of guiding the optical signal conduit through a sharp bend) has already been mentioned. It would also be possible to use water-tight optical signal transfer fittings to permit a new customer to tap into an optical signal conduit that has already been installed in a pipe section. For this, springs in the nature of FIG. 8 would need to have been installed previously, both upstream and downstream of the new customer's location, in order for the workmen who are installing the new tap to draw enough of the optical signal conduit from either side to connect a water-tight optical signal transfer fitting. The fitting itself might be similar to the one shown in FIG. 3, modified to accommodate two fibers (perhaps by employing a deep pair of narrow slots that extend from opposite sides of the sealing member 160 towards its center, with the slots spiraling from one end of the member 160 to the other, somewhat like a candy cane with slots instead of colored stripes). In order to accommodate future new customers, the workmen should install springs of the type shown in FIG. 8, both upstream and downstream of the new tap.

[0043] It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims. 

What I claim is:
 1. A method for installing an optical communication conduit, comprising: boring a first hole through a section of pipe that carries a fluid; boring a second hole through the section of pipe at a position spaced apart from the first hole; introducing the optical communication conduit into the section of pipe through one of the holes; and threading the optical communication conduit through the section of pipe toward the other hole.
 2. The method of claim 1, wherein the step of threading the optical communication conduit through the section of pipe comprises the steps of attaching the optical signal conduit to an elongated guide strip, introducing the guide strip into the section of pipe through one of the holes, and moving the guide strip between the holes.
 3. The method of claim 1, further comprising the steps of connecting the optical communication conduit to a fluid-tight optical signal transfer fitting, and attaching the fluid-tight optical signal transfer fitting to the section of pipe at the second hole.
 4. The method of claim 3, wherein the section of pipe is a section of a pipeline which additionally includes another section of pipe and a valve between the sections of pipe, wherein the second hole is bored adjacent the valve, and further comprising the steps of boring a third hole in the another section of pipe adjacent the valve, threading another portion of the optical signal conduit into the another section of pipe, connecting the another portion of the optical signal conduit to another fluid-tight optical signal transfer fitting, and attaching the another fluid-tight optical signal transfer fitting to the another section of pipe at the third hole.
 5. The method of claim 4, further comprising the step of connecting a valve-bypass segment of the optical signal conduit between the fluid-tight optical signal transfer fittings.
 6. The method of claim 4, further comprising the step of connecting a local signal distribution unit to the optical signal conduit in the sections of pipe via the fluid-tight optical signal transfer fittings, the local signal distribution unit providing customers with access to the optical communication conduit.
 7. The method of claim 6, wherein the local signal distribution unit comprises an optical coupler.
 8. The method of claim 1, further comprising the step of introducing, into the section of pipe, means for taking up slack in the optical signal conduit, the means for taking up slack being introduced through one of the holes.
 9. The method of claim 1, further comprising the step of attaching a fluid-tight optical signal transfer fitting to the section of pipe at the second hole, the optical communication conduit passing through the second hole via the fluid-tight optical signal transfer fitting.
 10. The method of claim 1,wherein the optical signal conduit threaded through the section of pipe is a single optical fiber.
 11. The method of claim 1, wherein the optical fiber is unjacketed, and hence exposed to the fluid.
 12. The method of claim 1, wherein the fluid is water and the segment of pipe is a segment of a water main.
 13. An optical signal communication conduit installed in the water main by the method of claim
 12. 14. A method for installing an optical communication conduit, comprising: boring a first hole through a section of a water main that carries potable water to customers; boring a second hole through the section of the water main; introducing the optical communication conduit into the section of the water main through one of the holes; attaching a first water-tight optical signal transfer fitting to the section of the water main at the first hole, with the optical signal conduit passing through the first water-tight optical signal transfer fitting; and attaching a second water-tight optical signal transfer fitting to the section of the water main at the second hole, with the optical signal conduit passing through the second water-tight optical signal transfer fitting.
 15. The method of claim 14, wherein the optical signal conduit comprises at least one optical fiber.
 16. The method of claim 15, wherein the at least one optical fiber is unjacketed, so that the at least one optical fiber is exposed to the water carried by the water main.
 17. The method of claim 15, further comprising the step of connecting the at least one optical fiber to a local signal distribution unit that is disposed outside the water main.
 18. The method of claim 14, wherein the water main also has another section, and a valve between the sections of the water main, wherein the second hole is bored adjacent the valve adjacent the valve, and further comprising the steps of boring a third hole in the another section of the water main, threading another portion of the optical signal conduit into the another section of the water main, and attaching a third water-tight optical signal transfer fitting to the another section of the water main at the third hole.
 19. An optical communication conduit installed in a water main by the method of claim 18, wherein the second and third water-tight optical signal transfer fittings are linked outside the water main by means for transferring optical signals.
 20. An optical communication conduit installed in a water main by the method of claim
 14. 